Systems and methods for controlling a conveyor system during product changeovers

ABSTRACT

System for controlling a conveyor system in a wallboard production line, including a computer processor and a deadband tuning module for controlling at least one of a line speed of a conveyor belt, a foam air amount for a slurry, and an amount of water deposited into a mixer. The deadband tuning module calibrates and sets a hysteresis threshold value based on input data of at least one of the line speed, the foam air amount, and the amount of water. The input data is collected over a predetermined period. A database is provided for storing at least one statistical information of the input data during the predetermined period. The deadband tuning module determines a deadband range based on the hysteresis threshold value and the at least one statistical information using the processor.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a Divisional application of U.S. patentapplication Ser. No. 14/481,358 filed Sep. 9, 2014, which isincorporated herein by reference in its entirety. The presentapplication also claims priority under 35 U.S.C. § 119(e) from U.S.Provisional Application Ser. No. 61/884,618, filed Sep. 30, 2013, whichis also incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure generally relates to systems and methods forpreparing cement or gypsum products, and more particularly relates toimproved systems and methods for controlling a line speed of a conveyorsystem during product changeovers in a wallboard production line.

Conventionally, gypsum products, such as calcium sulfate dihydrate, areprepared with typical basic ingredients, including calcined gypsum, suchas calcium sulfate hemihydrate or anhydrite, and water. A slurry mixeris typically used for supplying agitated gypsum slurry to the wallboardproduction line. Several types of gypsum wallboard manufacture aredescribed in co-assigned U.S. Pat. Nos. 6,494,609 and 6,986,812; both ofwhich are incorporated by reference.

As is well known in the art, a mixer is provided for uniformlydispersing calcined gypsum into water to form a slurry, and then theslurry is cast into a desired shaped mold or onto a surface to allow theslurry to set and form hardened gypsum by chemical reaction of thecalcined gypsum with water. A lightweight gypsum product is provided byuniformly mixing aqueous foam into the slurry to produce air bubbles.This results in a uniform distribution of voids in the set gypsumproduct when the bubbles are confined in the slurry before the gypsumhardens.

As the slurry travels downstream toward a forming plate on a conveyorsystem, a thickness of the slurry is determined by a predeterminedlocation of the forming plate above a conveyor belt. Depending on a massrate of the slurry traveling on the conveyor belt relative to a linespeed of the conveyor system, maintaining a generally laminar flow ofthe slurry before the forming plate is not readily achievable. Anoptimal line speed generally refers to a maximum possible speed that theconveyor system can support without forming a disruptive slurry headimmediately before the forming plate.

When the line speed is too fast relative to the mass rate of the slurrytraveling on the conveyor belt, excessive slurry that cannot passthrough the forming plate creates the slurry head in front of theforming plate, causing uneven accumulation and frequent clogging of theforming plate in the production line. Specifically, when the productchangeover is initiated, a composition or density rate of the gypsumproduct changes and also alters the mass rate of the slurry based on theproduct changeover requirements.

Therefore, there is a need for controlling the line speed of theconveyor system during the product changeovers such that the optimalline speed is maintained for the laminar flow of the slurry.

As the slurry advances on the conveyor belt, and is deposited betweentwo paper liners below the forming plate, a thickness of the wallboardbeing formed is equalized. After passing through the forming plate, theformed wallboard continues to travel on the conveyor belt for apredetermined period to allow the gypsum in the wallboard to set. Next,the set continuous strip of wallboard is cut into predetermined lengths,forming panels or boards, and each cut board then passes through ahydration section and subsequently a drying section having an oven orkiln on single or multiple decked roller conveyors, such that heated airis blown across an upper and lower faces of the board for drying.

However, when gaps between adjacent boards are too wide, exposed edgesof the board become parched or toasted by the heated air, and thetoasted edges tend to warp, buckle, pop, crumble or otherwise distortthe board due to uneven drying. As a result, the boards are sent throughthe drying kiln side-by-side or end-to-end to reduce the exposed edgesand any associated distortions of the boards. While the hydrationsection and the drying section are part of the conveyor system as awhole, each section has its own line speed for the correspondingconveyor belt.

Therefore, there is a need for controlling the line speed of theconveyor system for the cut wallboard panels going into the kiln suchthat the adjacent boards are touching each other in an end-to-endrelationship to prevent toasting the edges during heat treatment.

SUMMARY

The present disclosure is directed to systems and methods forcontrolling a line speed of a conveyor system during product changeoversin a wallboard production line. One aspect of the present control systemis that, as described in further detail below, a volumetric buildup ofthe slurry head at the forming plate is controlled by automaticallyadjusting the line speed of the conveyor system based on a distance tothe slurry head measured by a laser sensor. Positioned near the formingplate, the laser sensor determines whether the buildup of the slurryhead is located within a predetermined distance. Based on the distancebetween the slurry head and the sensor, the line speed of the conveyorsystem is adjusted.

Another important aspect is that the present control system operatesthrough a computer algorithm to control the line speed of the conveyorsystem for adjusting a mixer output as an additional volumetric controlof the slurry. More specifically, the present control system adjusts theline speed of the conveyor system during a running change of theproducts in the wallboard production line for inhibiting disruptioncaused by the change in mass rate of the stucco/gypsum materials. Thedisruption causes an overflow in a mixer output, resulting in acondition known as “overshoot.” Adjusting the line speed of the conveyorsystem provides a linear variation of the mass rate change, and reducesor eliminates the overshoot during the changeover period.

In yet another aspect, the present control system adjusts the line speedof the conveyor system for the cut wallboard panels that are sentthrough the drying kiln. A conventional optical switch is used tomeasure a gap between adjacent wallboard panels together with anassociated length of each wallboard panel for calculating apredetermined line speed of the conveyor system based on the measuredgap and length. Closing the gap between the adjacent panels is achievedby implementing the calculated line speed in the conveyor system.Consequently, an amount of wallboard waste during the heat treatment ofthe boards is reduced, and a structural integrity of the wallboard ispreserved.

In one embodiment, after one year trial period of the present controlsystem, it has been discovered that a main programmable logic controldelay of the conveyor system has been reduced by approximately 92%, awet slurry waste has been reduced by approximately 54%, and an amount ofdry ingredient waste, such as the calcined gypsum, has been reduced byapproximately 7%. Specifically, a volume of the slurry introduced to theconveyor system has been maintained consistently during the changeoverperiod, and as a result, the present control system reduced a number ofproduction interruptions, and waste materials, thereby reducing overalloperational costs and delay time.

More specifically, a system is provided for controlling a line speed ofa conveyor belt of a conveyor system during product changeovers in awallboard production line. Included in the system are a computerprocessor, a central control module for controlling operation of aposition sensor and a database. The position sensor is located on top ofa conveyor table for providing positional information of a slurry headformed in front of a forming plate of the conveyor system. A positiondetection module is provided for receiving a position signal from theposition sensor, and determining whether the slurry head is locatedwithin a predetermined distance relative to the position sensor based onthe position signal. A speed adjustment module is provided forregulating the line speed of the conveyor belt based on the positionsignal using the processor.

In another embodiment, a system is provided for controlling a line speedof a conveyor belt of a conveyor system during product changeovers in awallboard production line. Included in the system are a computerprocessor, a calculation module for calculating a predetermined massrate of a supply of ingredients transported on the conveyor belt anddeposited into a mixer during a product changeover period, a speedadjustment module for adjusting the line speed of the conveyor belt,using the processor, based on at least one of the predetermined massrate and the line speed of the conveyor belt for reducing an overshootduring said product changeover period.

In yet another embodiment, a system is provided for controlling aconveyor system in a wallboard production line, including a computerprocessor and a deadband tuning module for controlling at least one of aline speed of a conveyor belt, a foam air amount for a slurry, and anamount of water deposited into a mixer. The deadband tuning modulecalibrates and sets a hysteresis threshold value based on input data ofat least one of the line speed, the foam air amount, and the amount ofwater. The input data is collected over a predetermined period, adatabase is provided for storing at least one statistical information ofthe input data during the predetermined period; and wherein the deadbandtuning module determines a deadband range based on the hysteresisthreshold value and the at least one statistical information using theprocessor.

In still another embodiment, a system is provided for controlling a linespeed of a conveyor belt of a conveyor system in a wallboard productionline, and includes a computer processor, a hydration section for storinga plurality of wallboard panels cut by a cutter, a drying section havinga drying kiln for drying the plurality of wallboard panels, and abutting switch disposed in the hydration section at a predetermineddistance from the drying section for measuring a gap between adjacentwallboard panels and a longitudinal wallboard length. The conveyor beltin the hydration section is operated at a hydration section speed, andthe conveyor belt in the drying section is operated at a drying sectionspeed, the hydration and drying section speeds are set differently. Acalculation module is provided for calculating a predetermined gapadjustment value based on at least one of the hydration section speed,the drying section speed, said gap, and the longitudinal wallboardlength; and a speed adjustment module is provided for adjusting the linespeed of the conveyor belt in the hydration and drying sections based onthe gap adjustment value using the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic elevation view of a partial wallboardproduction line suitable for use with the present control system,featuring a slurry mixer;

FIG. 2 is a functional block diagram of the present control systemfeaturing functional modules;

FIGS. 3 and 4 are graphical representations of an exemplary mass ratechange during a product changeover period;

FIG. 5 is a diagrammatic elevation view of a partial wallboardproduction line suitable for use with the present control system,featuring a drying kiln; and

FIGS. 6A-6C illustrate an exemplary control method in accordance with anembodiment of the present control system.

DETAILED DESCRIPTION

Referring now to FIG. 1, the present control system is generallydesignated 10, and is designed to control a line speed of a conveyorsystem, generally designated 12, in a wallboard production line 14. Amixer 16 configured for mixing and dispending a slurry is disposed abovethe production line 14 that includes a conveyor table 18 upon which aweb of face paper 20 is moved on a conveyor belt 22 in a direction oftravel designated by the arrow T. A supply of stucco 24 having variousingredients is delivered to the mixing for deposition upon the facepaper 20 located on the conveyer belt 22.

While a variety of settable slurries are contemplated, the presentcontrol system 10 is particularly designed for producing stucco/gypsumpanels. In many applications, the slurry is formulated to includevarying amounts of gypsum, aggregate, water, accelerators, plasticizers,foaming agents, fillers, cement, and/or other ingredients well known inthe art. The relative amounts of these ingredients, including theelimination of some of the above or the addition of other ingredients,may vary to suit requirements for a particular product.

A web of top or backing paper 26 is also moved above the conveyor belt22 in the direction T, sandwiching the slurry between the face and toppapers 20, 26 beneath a forming plate 28 for shaping and molding awallboard 30. A spout 32 attached to the mixer 16 is located upstream onthe wallboard production line 14, and the slurry is dispensed from thespout on the web of face paper 20 during operation of the conveyorsystem 12. A slurry head 34 is formed in front of the forming plate 28,and is detected by a position sensor 36, such as a laser emitter, formeasuring a distance D between the slurry head and the position sensor.Based on the distance D, the control system 10 adjusts the line speed ofthe conveyor belt 22, and also controls a volumetric output of theslurry dispensed from the mixer 16 based on the line speed.

An important feature of the present control system 10 is that the slurrydispensing operation is controlled by a line speed control system,generally designated 38. In a preferred embodiment, the line speedcontrol system 38 is a software installed computer device havingprogrammable modules for various functions. As used herein, the term“module” may refer to, be part of, or include an Application SpecificIntegrated Circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group), a programmable logic controller (PLC) and/ormemory (shared, dedicated, or group) that execute one or more softwareor firmware programs, a combinational logic circuit, and/or othersuitable components that provide the described functionality.

As is known in the art, the module may be implemented with aproportional-integral-derivative (PID) controller, and other variations,such as proportional-integral, proportional-derivative, and proportionalcontrollers, as either stand-alone controllers or configurable softwaremodules within the present control system 10. Another important featureof the present control system 10 is that any module can be tuned andconfigured to have an adjustable deadband range. Tuning algorithmsinclude, but not limited to, non-parametric methods, such as aconventional closed-loop tuning method or relay feedback test to providea satisfactory and consistent performance in the presence of measurementnoise and varying disturbances. A more detailed description of thetuning algorithm is provided below in discussion relating to FIG. 2.

Although the children modules residing in their respective parentmodules are shown, the broad teachings of the present system can beimplemented in a variety of forms. Thus, while this disclosure includesparticular examples and arrangements of the modules, the scope of thepresent device should not be so limited since other modifications willbecome apparent to the skilled practitioner.

Referring now to FIGS. 1 and 2, it is preferred that the present linespeed control system 38 includes a central control module (CCM) 40, theposition sensor 36, and a database 42. Overall operation of the linespeed control system 38 is controlled by the CCM 40. Positionalinformation of the slurry head 34 is provided by the position sensor 36located preferably on top of the conveyor table 18. All relevantinformation can be stored in the database 42 for retrieval by the CCM40, e.g., as a data storage device and/or a machine readable datastorage medium carrying computer programs.

Also included in the CCM 40 is an interface module 44, which provides aninterface between the CCM 40, the position sensor 36, and the database42. The interface module 44 also controls operation of, for example,conveyor belt motors 46, and other related system devices, services, andapplications. The other devices, services, and applications may include,but are not limited to, one or more software or hardware components, asare known in the art. The interface module 44 also receives signals,which are communicated to the respective modules, such as the CCM 40 andits children modules 44, 47, 48, 50, 52, 54.

Regarding the children modules 44, 47, 48, 50, 52, 54, each child modulecan be tuned by a deadband tuning module 47. While the deadband tuningmodule 47 is shown to control a line speed of the conveyor belt 22 and afoam air amount for the slurry in the FIG. 2 embodiment, the deadbandtuning module 47 can be used for modules controlling other devices, suchas a water pump (not shown) for the mixer 16. More specifically, ahysteresis threshold value HYS is calibrated and set by the deadbandtuning module 47 using calibration software based on input data DATA. Asan example only, in the case of the water pump, the input data DATArefer to relevant information about an amount of water deposited intothe mixer 16, and are collected in the database 42 by the CCM 40 over apredetermined period, e.g., 2-3 minutes. Statistical information, suchas a minimum, a maximum, and an average amount of water are calculatedand saved in the database 42 during the predetermined period. Thehysteresis threshold value HYS is determined based on a statisticalnormal distribution of the collected input data DATA.

In a preferred embodiment, a steady-state control value, two to threetimes the standard deviation of the input data DATA, is used fordetermining the deadband range such that the measurement noise orquantization noise, and other similar changes do not cause frequent,unstable oscillating or repeated changes in the amount of waterdelivered to the mixer 16. An exemplary deadband range DEADBAND may bedefined as provided by expression 1.

DEADBAND=f{HYS,DATA}  (1)

An automatic adjustment of the deadband range DEADBAND is achieved bycalculating the hysteresis threshold value HYS based on at least one ofthe statistical data, such as the minimum, maximum, average, andstandard deviation values via the deadband tuning module 47. However,the deadband range DEADBAND can also be calibrated and overriddenmanually for locking in the deadband range at a desired offset from apredetermined value based on the input data DATA. Although the deadbandtuning module 47 is shown as a child module of the CCM 40, the deadbandtuning module 47 can be incorporated into the other embodiments of thepresent control system 10 as a separate, independent control system.

A position detection module 48 receives a position signal P from theposition sensor 36 via the interface module 44, and determines whetherthe slurry head 34 is located within a predetermined distance relativeto the position sensor based on the position signal P. During a productchangeover, the slurry density and/or the composition rate of the stuccoand water are changed based on product changeover requirements. Forexample, a wallboard “A” production line comes to an end, and theconveyor system 12 prepares for a wallboard “B” production line bymodifying amounts of stucco and water mixed in the mixer 16. A variationin the amounts of stucco and water triggers a change in the slurrydensity and/or the composition rate, and consequently alters thedistance D between the slurry head 34 and the position sensor 36.

Controlling an amount and a location of the slurry head 34 accumulatingnear the forming plate 28 is achieved by adjusting the line speed of theconveyor belt 22. A speed adjustment module 50 is provided forregulating the line speed of the conveyor belt 22 in response to theposition signal P. It is preferred that a foam air control module 52 isalso provided for controlling an amount of air mixed into the slurry inresponse to the position signal P. Mixing aqueous foam into the slurryto produce air bubbles is also an effective way of controlling theslurry head 34. Although the speed adjustment module 50 and the foam aircontrol module 52 can be separately executed, both modules 50, 52 arepreferably simultaneously executed in tandem during the productchangeover.

Another important aspect of the present line speed control system 38 isthat it reduces any disruption caused by the change in mass rate of thestucco/gypsum materials entering into the mixer 16. A desired result ofthe line speed control system 38 is maintaining a steady, consistentmass rate during the changeover period. An abrupt mass rate changeduring the product changeover period causes an overshoot in a mixeroutput. Changing the line speed of the conveyor system 12 provides alinear variation of the mass rate change, and consequently reduces oreliminates the overshoot.

In a preferred embodiment, a calculation module 54 is provided forcalculating a predetermined mass rate MASS and a predetermined linespeed LNSPD. The mass rate MASS refers to a desired mass rate ofingredients, such as stucco 24, transported on the conveyor belt 22 anddeposited into the mixer 16 during the product changeover period. Asdescribed in further detail below, the mass rate MASS is determinedbased on at least one of a first ingredient mass rate IMR1, and acurrent conveyor line speed CLS. An exemplary mass rate MASS may bedefined as provided by expression 2.

MASS=f{IMR1,CLS}  (2)

As for the line speed LNSPD, it refers to a desired line speed of theconveyor belt 22 upon which the ingredients are transported upstream onthe production line 14 toward the mixer 16 during the product changeoverperiod. The line speed LNSPD is determined based on at least one of thefirst ingredient mass rate IMR1 and a second ingredient mass rate IMR2.An exemplary line speed LNSPD may be defined as provided by expression3.

LNSPD=f{IMR1,IMR2}  (3)

Adjusting the line speed of the conveyor belt 22 based on at least oneof the mass rate MASS and the line speed LNSPD provides a smoothtransition during the product changeover period.

Referring now to FIG. 3, a graphical illustration of exemplary stuccomass rate changes is shown during the product changeover period when theline speed of the conveyor belt 22 is not controlled by the line speedcontrol system 38. In some applications, the product changeover requirestransportation of stucco 24 having a higher mass rate than before thechangeover period. Typically, a first mass rate change 56, measured inpound per thousand square feet (lb/msf), exhibits a linear increasingslope 58 during a changeover period TIME defined by time between a firstsetpoint 60 and a second setpoint 62, indicating a steady flow of thestucco 24 being transported on the conveyor belt 22. However, a secondmass rate change 64, measured in pound per minute (lb/min), correspondsto a non-linear parabolic curve 66, indicating presence of theovershoot.

Referring now to FIG. 4, the graphical illustration of FIG. 3 is shownwhen the line speed of the conveyor belt 22 is controlled and adjustedby the present line speed control system 38. Components shared with FIG.3 are designated with identical reference numbers. A major differencefeatured in this figure is that the second mass rate change 64corresponds to a linear flat line 68, indicating absence of theovershoot. Avoidance of the overshoot is achieved by adjusting the linespeed of the conveyor belt 22 for sustaining the mass rate change 64linear or constant. As discussed above, the line speed of the conveyorbelt 22 is adjusted based on at least one of the mass rate MASS and theline speed LNSPD, both of which are calculated by the calculation module54.

Returning to the expressions (2) and (3) described above, the firstingredient mass rate IMR1 refers to a mass rate of the ingredient orstucco 24, transported on the conveyor belt 22 during the productchangeover period, and is measured in pound per thousand square feet(lb/msf). Similarly, the second ingredient mass rate IMR2 refers to themass rate of the identical stucco 24 transported during the changeoverperiod, and is measured in pound per minute (lb/min). Exemplary secondingredient mass rate IMR2 and line speed LNSPD may be defined asprovided by expressions 4 and 5.

$\begin{matrix}{{{IMR}\; 2} = {{IMR}\; 1*{LNSPD}*\frac{W}{CONV}}} & (4) \\{{LNSPD} = {\frac{{IMR}\; 2}{{IMR}\; 1}*\frac{CONV}{W}}} & (5)\end{matrix}$

where W denotes a width of the wallboard 30, e.g., 4 feet, and CONVdenotes a conversion factor for the unit used in IMR1 (msf), i.e.,1,000.

An important aspect of the line speed control system 38 is that thesecalculations are performed automatically by the calculation module 54during the product changeover period TIME, and the line speed of theconveyor belt 22 is adjusted to the calculated line speed LNSPD by thespeed adjustment module 50 for providing a smooth transition of therunning change in the wallboard production line 14 during the productchangeover period.

Referring now to FIGS. 1 and 5, as the slurry passes through the formingplate 28, the wallboard 30 is formed and continues to travel on theconveyor belt 22 in the direction T for a predetermined period to allowsetting for gypsum of the wallboard. A cutter 70 is provided for cuttinga continuous strip of wallboard 30 at a predetermined length L, and theneach cut board segment or panel 72 is sequentially stacked up on one ormore decks 74 disposed in a hydration section 76.

Included in the hydration section 76 is a butting switch 78, such as anoptical switch, disposed at a predetermined distance, e.g., 40 feet,from a drying section 80, having a drying oven or kiln 82. The buttingswitch 78 is disposed on at least one of the decks 74, and is used tomeasure a gap G between adjacent board segments 84, 86, and thepredetermined board length L. Another important aspect of the presentline speed control system 38 is that the butting control can beperformed using a single butting switch 78 disposed on a single deck 74.

Each section 76, 80 has its own different line speed for thecorresponding conveyor belt 22. Specifically, the hydration section 76is operated at a hydration section speed HS_(SPD), and the dryingsection 80 is operated at a drying section speed DS_(SPD). Feeding theboard segments 72 into the drying kiln 82 in the end-to-end relationshipis achieved by adjusting the line speed of the conveyor belts 22 in atleast one of the hydration and drying sections 76, 80. Morespecifically, the calculation module 54 calculates a predetermined gapadjustment value GAP_(ADJ) based on at least one of the hydrationsection speed HS_(SPD), the drying section speed DS_(SPD), the gap Gbetween adjacent boards 84, 86, and the predetermined board length L. Anexemplary gap adjustment value GAP_(ADJ) may be defined as provided byexpression 6.

GAP_(ADJ)=f{HS_(SPD),DS_(SPD),G,L}  (6)

where a positive GAP_(ADJ) automatically causes an increase of the gap Gby providing less butting of the adjacent boards 84, 86, and a negativeGAP_(ADJ) automatically causes a decrease of the gap G by providing morebutting of the adjacent boards 84, 86, such that the adjacent boards inthe drying kiln 82 are closer to each other. Next, the speed adjustmentmodule 50 adjusts the line speed of the conveyor belts 22 in eachsection 76, 80 based on the gap adjustment value GAP_(ADJ).

Referring now to FIGS. 6A-6C, an exemplary method of the control system10 is shown using the present line speed control system 38. Although thefollowing steps are primarily described with respect to the embodimentsof FIGS. 1-5, it should be understood that the steps within the methodmay be modified and executed in a different order or sequence withoutaltering the principles of the present disclosure.

The method begins at step 100. In step 102, the CCM 40 initiatesoperation of the line speed control system 38, and activates itschildren modules 44, 47, 48, 50, 52, 54, and other associated devices.More specifically, the interface module 44 initiates communicationsbetween the CCM 40 and peripheral software and hardware components, suchas the position sensor 36, the database 42, and the conveyor belt motors46.

In step 104, the CCM 40 determines whether the changeover period hasstarted. If the changeover period has begun, control proceeds to step106. Otherwise, control proceeds to step 108. In step 106, the positiondetection module 48 receives a position signal P from the positionsensor 36 via the interface module 44. In step 110, the positiondetection module 48 determines a location of the slurry head 34 relativeto the position sensor 36 based on the position signal P, and generatesa distance value D. If the distance value D is greater than apredetermined distance D_(PRE), control proceeds to step 106. If thedistance value D is less than or equal to the predetermined distanceD_(PRE), control proceeds to steps 112 and/or 114.

In step 112, the speed adjustment module 50 regulates the line speed ofthe conveyor belt 22 based on at least one of the position signal P andthe distance value D. In step 114, the foam air control module 52controls an amount of air mixed into the slurry based on at least one ofthe position signal P and the distance value D. Both steps 112, 114 canbe performed simultaneously, separately, or in a partial combination asrequired to suit the situation. For example, the line speed of theconveyor belt 22 and the amount of air mixed into the slurry can beadjusted sequentially or alternatively.

In step 116, the calculation module 54 calculates the predetermined massrate MASS and the predetermined line speed LNSPD based on at least oneof the first ingredient mass rate IMR1, the second ingredient mass rateIMR2, and the current conveyor line speed CLS. In step 118, the speedadjustment module 50 adjusts the line speed of the conveyor belt 22based on at least one of the predetermined mass rate MASS and line speedLNSPD.

In step 120, the CCM 40 determines whether the changeover period hasended. If the changeover period has ended, control proceeds to step 122.Otherwise, control returns to step 106 to continue monitoring theposition of the slurry head 34. In step 122, the CCM 40 deactivates theline speed control system 38, and control ends at step 124.

Returning to step 104, when the changeover is not detected by the CCM40, control proceeds to step 108. In step 108, the CCM 40 determineswhether the wallboard segments or panels 72 are entering into thehydration section 76. If the wallboard segments or panels 72 are sent tothe hydration section 76 by the conveyor system 12, control proceeds tostep 126. Otherwise, control proceeds to step 104 to determine whetherthe changeover period has started.

In step 126, the position detection module 48 measures the gap G betweenthe adjacent board segments 84, 86, and the predetermined board length Lbased on a butting switch signal BS generated from the butting switch78, and an elapsed time ET. The elapsed time ET refers to a time periodbetween a first detection of a wallboard segment edge 88 and a seconddetection of another segment edge 88. A shorter period may indicatedetection of the gap G, and a longer period may indicate detection ofthe board length L based on how long the butting switch 78 is activated(turned on) and deactivated (turned off) for.

In step 128, the calculation module 54 calculates the predetermined gapadjustment value GAP_(ADJ) based on at least one of the hydrationsection speed HS_(SPD), the drying section speed DS_(SPD), the gap Gbetween adjacent boards 84, 86, and the predetermined board length L. Instep 130, the speed adjustment module 50 adjusts the line speed of theconveyor belts 22 in each section 76, 80 based on the gap adjustmentvalue GAP_(ADJ). Control proceeds to step 104.

While a particular embodiment of the present line speed control systemhas been described herein, it will be appreciated by those skilled inthe art that changes and modifications may be made thereto withoutdeparting from the present disclosure in its broader aspects.

What is claimed is:
 1. A system for controlling a conveyor system in awallboard production line, comprising: a computer processor; a deadbandtuning module for controlling at least one of a line speed of a conveyorbelt, a foam air amount for a slurry, and an amount of water depositedinto a mixer; wherein said deadband tuning module calibrates and sets ahysteresis threshold value based on input data of at least one of saidline speed, said foam air amount, and said amount of water, said inputdata being collected over a predetermined period; a database for storingat least one statistical information of said input data during thepredetermined period; and wherein said deadband tuning module determinesa deadband range based on said hysteresis threshold value and said atleast one statistical information using the processor.
 2. The system ofclaim 1, wherein said deadband tuning module determines said hysteresisthreshold value based on at least one of minimum, maximum, average, andstandard deviation values of said input data.
 3. The system of claim 1,wherein said deadband range is calibrated and overridden manually forlocking in said deadband range at a desired offset from a predeterminedvalue based on said input data.